High quality headphones for reproducing stereophonically recorded programs often have earpieces which have individual volume-balance controls to allow the listener to make fine adjustments in both the volume level and the stereo balance without having to remove the earpieces or to adjust the receiver or the amplifier.
One type of control which has been employed in headphone earpieces is the conventional rotary-type control in which an indexing dial is friction fit directly to the control shaft of a potentiometer which controls the volume-balance output of an audiotransducer positioned in the earpiece. To permit manipulation of the control from outside the earpiece, a portion of the indexing dial extends through an opening in the cover of the earpiece.
The use of such conventional rotary-type controls for headphone earpieces has not been completely satisfactory because at times the indexing dial is not perfectly centered in the opening of the earpiece cover. When this occurs, the dial as it is rotated may contact the sides, top or bottom of the opening making fine adjustment difficult. The indexing dial may be imperfectly centered in the opening because the control shaft of the mass produced potentiometer is not perfectly perpendicular to the body of the potentiometer. Another reason this may occur is that although the control shaft is perpendicular to the body of the potentiometer, the potentiometer itself may be imperfectly positioned in the base of the earpiece and as a result the indexing dial which is friction fit tightly to the shaft may be canted so that it is not centered in the opening in the cover.